The Study On The Effects Of Titanium Dioxide Nanoparticles On Reducing Phoxim-induced Toxicity On The Silkworm (Bombyx Mori)

Organophosphorus pesticides, one kind of phosphorus-containing compound, arewidely used to control the agricultural and forestry pests. Nowadays, organophosphoruspesticides have been widely used to control Mulberry pests, but due to the irrational timearrangement of the production plan and the irrational agricultural industrial structure,phoxim makes forays into the mulberry plantations, thereby severely affecting the survivalof the silkworm (Bombyx mori, B. mori) for main mulberry consumer. Due to the long timeartificial selection, silkworm had weak resistance on chemical pesticides, thus the carelessuse of pesticides caused a serious impact on the economic development of sericultureevery year. Titanium dioxide nanoparticles (TiO2NPs) are widely used in variousmanufactured products, including sunscreen, pharmaceuticals, toothpaste, white pigment,cosmetics and environmental decontamination of air, soil and water. Their structural unitsize are between1nm to100nm, and the small size, large surface area and macroscopicquantum tunneling effects endow them with the functions of antibacterial, anti-UV,self-cleaning and so on.In order to investigate whether TiO2NPs can reduce the phoxim-induced toxicity onsilkworm, and then reduce the loss of sericulture, in the present study we used the larvae ofB. mori (B. mori Qiufeng×Baiyu) to investigate the effects of TiO2NPs (5mg/L) onreducing phoxim (4.2μg/mL)-induced silkworm protein metabolism and carbohydratemetabolism toxicity, and analysed the effects of TiO2NPs on reducing the genetranscription and physiological function altering under phoxim exposure in the brain andsilk gland of B. mori via digital gene expression (DGE) profiling techniques. The mainresults are as follows:1. TiO2NPs relieve biochemical dysfunctions of B. mori under phoxim exposureWe used silkworm hemolymph as research materials, and explored phoxim-inducedsilkworm protein metabolism and carbohydrate metabolism toxicity of B. mori, and then analysed the effects of TiO2NPs on alleviating the phoxim toxicology of B. mori byadding TiO2NPs. The results demonstrated that added TiO2NPs significantly decreasedreduction of protein, glucose and pyruvate contents, lactate dehydrogenase, succinatedehydrogenase and malate dehydrogenase activities, increased by56.7%,32.2%,41.5%,81.6%,74.9%and83.7%respectively, and attenuated increases of free amino acids, urea,uric acid and lactate levels, activities of protease, alanine aminotransferase and aspartateaminotransferase in the hemolymph of silkworms caused by phoxim exposure.2. Molecular mechanisms of reduced nerve toxicity by TiO2NPs in the phoximexposure brain of B. moriWe used silkworm brain as research materials, and explored whether TiO2NPstreatment can reduce the phoxim-induced brain damage of B. mori. We observed that TiO2NPs pretreatments relieved severe brain damage and oxidative stress under phoximexposure, relieved phoxim-exposed ACh, Glu and NO contents increasing and NE, DA,and5-HT contents decreasing, and decreasing the inhibition of AChE, Na+/K+-ATPase,Ca2+-ATPase, and Ca2+/Mg2+-ATPase activities and TNOS activity increasing in the brain.Furthermore, DGE data suggested that phoxim exposure led to significant alterations in theexpression of295genes, while a combination of both phoxim and TiO2NPs treatmentresulted in marked changes in the expression of472genes, and qRT-PCR assay revealedthat TiO2NPs pretreatment inhibited the up-regulated expression of ace1, cytochrome-c,caspase-9, caspase-3, Bm109and down-regulated expression of BmIap caused by phoxim;these genes are involved in nerve conduction, oxidative stress and apoptosis. TiO2NPspretreatment also inhibited the down-regulated expression of H+transporting ATPsynthase and vacuolar ATP synthase under phoxim exposure, which are involved in iontransport and energy metabolism. These results indicate that TiO2NPs pretreatmentreduced the phoxim-induced nerve toxicity in the brain of B. mori.3. Molecular mechanisms of reduced silk gland damage by TiO2NPs in thephoxim exposure silk gland of B. moriWe used silkworm silk gland as research materials, and explored whether TiO2NPstreatment can reduce the phoxim-induced silk gland damage of B. mori. The resultsindicated that exposure to phoxim resulted in a significant silk gland damage, whereasTiO2NPs attenuated phoxim induced gland damage, increased the antioxidant capacity ofthe gland in B. mori. Furthermore, DGE data suggested that phoxim exposure led to significant alterations in the expression of833genes. In particular, phoxim exposurecaused significant down regulation of Fib-L, Ser2, Ser3, and P25involved in silk proteinsynthesis, and up-regulation of Sfgh, Uchl3, and Salhh involved in silk protein hydrolysis.A combination of both phoxim and TiO2NPs treatment resulted in marked changes in theexpression of754genes, while treatment with TiO2NPs led to significant alterations in theexpression of308genes. Importantly, pretreatment with TiO2NPs increased Fib-L, Ser2,Ser3, and P25expression, and decreased Sfgh, Uchl3, and Salhh expression in silk proteinin the silk gland under phoxim stress.This study illustrates the molecular mechanisms of reduced toxicology by TiO2NPsin the phoxim exposure larvae of B. mori, and provides new insights into alleviatingphoxim-exposed toxicology on B. mori, and provides reliable data for the industrialapplication of TiO2NPs in sericulture.